Media prepare for a ceremony at Dealey Plaza in Dallas Nov. 22, 2013, marking the anniversary of the assassination of President John F.Kennedy. / Larry W. Smith/epa

by Rick Jervis and Doug Stanglin, USA TODAY

by Rick Jervis and Doug Stanglin, USA TODAY

DALLAS - Thousands of people bowed their heads or clasped hands with loved ones in Dealey Plaza at 12:30 p.m. Friday to mark the precise moment 50 years ago that shots rang out to take the life of John F. Kennedy, the 35th president of the United States.

The silence was broken with the singing of America the Beautiful by the U.S. Navy choir.

The moment of reflection came midway through a solemn, 44-minute ceremony only steps from the site of the assassination on Nov. 22, 1963.

"He was ambitious to make it a better world - and so were we," historian David McCullough said before reading excerpts from Kennedy speeches.

"He spoke to to the point and with confidence," McCullough said. "He knew words matter. His words changed lives. His words changed history. And rarely has a commander in chief addressed the nation with such command of language."

The weather - cold with a light, freezing drizzle - was in stark contrast to that Friday in 1963, which started cloudy but broke into bright sunshine by midmorning, prompting the presidential motorcade to remove the clear-bubble protection atop the limousines.

Creating a silent backdrop to the ceremony was the red-brick building that once housed the Texas School Book Depository, where, according to the Warren Commission, Lee Harvey Oswald fired the rifle shot from a six-story window that killed the 46-year-old president.

Friday's event was by invitation only, and some lucky 5,000 guests were selected in a lottery system. Some arrived as early as 6 a.m. CT.

Samuel and Tammy Ramon of Fort Worth applied in June and were thrilled when they were selected. Though he was only 1 year old when Kennedy was shot, Samuel Ramon said being part of the 50th anniversary is something he'll someday tell his grandchildren and great-grandchildren about.

"He was a great president," said Samuel Ramon, bracing against the cold as he entered through security. "It makes me want to see where everything happened."

The ceremony began at 12:10 p.m. CT with a procession by a six-member bagpipes and drums band, followed by the national anthem by Monica Saldivar.

Dallas Mayor Mike Rawlings, who opened the ceremony, recalled the nightmare that took place "in our front yard."

"It seems we all grew up that day, city and citizens, and suddenly, we had to step up and try to live up to the envisions of our beloved president," he said.

Roy Widley, 67, of the Dallas suburb of Richardson, said he hoped the ceremony would, once and for all, distance Dallas from the tragic killing.

"He was slain right here, and the city's taken a lot of heat for that," he said. "A lone assassin killed the president, not Dallas."

Kerry Gonzalez, 46, took time off from being a homemaker in nearby Arlington to attend the ceremony.

The ceremony was a somber memorial to a president slain in his prime, she said. But it was also a tribute to the crowds - 200,000 by some estimates - who lined downtown Dallas that day five decades ago to cheer and support their president, she said.

"It's a good way to honor what happened 50 years ago today," Gonzalez said. "There was a lot of people out that day supporting the president. It wasn't a hateful place."

The ceremony was organized as a joint event between the President John F. Kennedy Commemorative Foundation and the city of Dallas.

The solemn, dignified mood at Dealey Plaza on Friday was markedly different than the confusion and chaos that reigned five decades ago as shots rang out and the presidential limo bolted forward to rush the stricken president to Parkland Hospital.

A large banner of JFK's portrait was erected as a backdrop for the main stage. The large white "X" that usually marks the spot where Kennedy was hit was paved on a day ago in advance of the ceremony.

Many of the familiar sites from that tragic day are still here. Network cameras were set up at the Commerce Street plaza, opposite the grassy knoll, the site of many assassination conspiracy theories.

The Coalition on Political Assassinations, which usually gathers on the knoll each Nov. 22, will not be allowed to meet at the site this year during the main event. Instead, The Dallas Morning News reports, the group will hold an event at the nearby JFK memorial, then move to the plaza after the ceremony is over.

The nearby Sixth Floor Museum, which chronicles the assassination and is located on the same floor where Oswald fired on the motorcade, will open from 3 to 8 p.m. CT, after the formal ceremony.

Elsewhere in Dallas, a brief morning ceremony, including the lowering of a flag to half-staff, was scheduled at Parkland Hospital, where Kennedy died.

The Texas Theatre, where police captured Oswald, will screen part of the movie War Is Hell, which was showing when the assassin slipped into the audience without paying on the afternoon of Nov. 22, 1963.

Other events around the country:

In Washington, U.S. Attorney General Eric Holder paid his respects shortly after sunrise at Kennedy's grave at Arlington National Cemetery.

In Hyannis, Mass., a wreath-laying ceremony was held at the John F. Kennedy Memorial in Veterans Memorial Park.

In Boston, the statue of John F. Kennedy was open for public viewing. A special Mass commemorating the assassination anniversary was planned at Blessed Sacrament Chapel, Cathedral of the Holy Cross.